1. Field of the Invention
This invention relates to the art of controlling air flow through door sash equipped apparatus in proportion to the degree of opening of the sash and particularly deals with sash operated damper controls for laboratory fume hoods.
2. Prior Art
In my prior U.S. Pat. No. 4,150,606 granted Apr. 24, 1979, entitled "Automatic Laboratory Fume Hood Sash Operator", I have described and claimed an attachment for laboratory fume hood structures which will open and close the movable sash member thereof. In this patent, switches, triggered by movement of the sash will drive an exhaust blower at high speeds when the sash is open, at low speeds when the sash is closed and may also drive an auxiliary blower when the sash is open. Proportioning of air flow between fully opened and fully closed sash positions is not provided. It would be an improvement in the art to control the exhaust system in proportion to the degree of opening of the door sash and to provide an individual damper control for each fume hood in an exhaust system serving an individual hood or in an exhaust system serving a plurality of fume hoods.